Tips from the clinical experts
Answering your questions
Edited By Brad S. Karon, MD, PhD
Pretransfusion plasma testing
Q Does plasma have to be typed, screened, and cross matched
for transfusion? I know plasma can be added to a volume of RBCs in a
patient, but matched packed RBCs cannot be added to a volume of plasma in a
patient. What is the difference?
A Pretransfusion testing consists of type, screen, and
cross match. Type means ABO and Rh testing. Screen is testing for the
unexpected red-cell antibodies. Cross match means compatibility testing
between patient’s plasma and donor packed red cell for transfusion. It is a
requirement by the AABB Standards for the Blood Banks and Transfusion
Services to type and screen all donors and components prepared from these
donations including plasma, platelets, cryoprecipitate, and red cells which
should be labeled for the ABO and Rh type. The packed red cells are cross
matched with the patient’s plasma to confirm the compatibility prior to
transfusion. This helps in the prevention of hemolytic-transfusion reactions
due to naturally occurring ABO antibodies and unexpected low-incidence
red-cell alloantibodies. A person with blood type A has anti-B in his
plasma/serum and one with blood type B has anti-A in the plasma/serum (see
Table 1).
Table 1.
These naturally occurring ABO antibodies are mostly IgM,
complement binding, reactive at 37°C, and the cause for acute
hemolytic transfusion reaction or hyperacute rejection if transfused or
transplanted with ABO mismatched red cell products or solid organs (e.g.,
kidney). The titer of these antibodies in plasma can range from 1:8 to 1:256
for anti-B and 1:8 to 1:2,048 for anti-A. The total blood volume is about
5,000 cc in an average 70-kg male. When transfusing platelets or
cryoprecipitate of 200-cc to 300-cc volume, ABO type may not matter for
transfusion purposes due to dilutional effect.
It is well known, however, that a high titer unit,
especially in a single-donor platelet, which may be large volume, can cause
significant hemolysis of the patient’s red cells (acute hemolytic
transfusion reaction). Therefore, many institutions try not to transfuse ABO
mismatched single-donor platelets. Cryoprecipitate, a pooled product of 10
or 20 small units with a chance of dilution of one or two high titer units
in it, however, can be safely transfused without worrying about the ABO type
and significant red-cell hemolysis. As far as fresh-frozen plasma (now
available also as plasma frozen within 24 hours), two or more units are
usually required for transfusion to correct coagulation abnormalities in a
bleeding patient, and ABO compatibility is a must (see Table 2).
Table 2.
* Refer to Table 1 for ABO compatibility of red cell and plasma products.
—Krishna Oza, MD
Department of Pathology
University of Arkansas for Medical Sciences
Little Rock, AR
Post-vasectomy semen analysis
Q The physicians in our practice who perform vasectomies
are requesting sperm count — if sperm is present — so they know whether the
sperm count is going down on the patients’ post-vasectomy (PV) specimen.
Would it be reasonable to report the number of sperm per high-power field
(HPF) or in 10 high-power fields? How should post-vasectomy semen analysis
be performed and reported?
A Confirmation of azoospermia is important to establish
success of a vasectomy. Typically, two semen samples are tested at least six
to eight weeks after the vasectomy. While the World Health Organization
provides a guide for establishing azoospermia, a specific procedure for
performing and reporting post-vasectomy semen analysis is not provided.1
Semen analysis for PV samples involves two steps: an
initial analysis of the neat semen sample for presence of sperm, followed by
centrifugation at 1,000 x g for 15 minutes if no sperm are seen in the
ejaculate. It is important to examine a minimum of 30 HPFs (40x
magnification) for both the ejaculate and the pelleted sample. Results are
reported for motility and number of sperm seen per HPF.
While most PV samples will have either no sperm or will
require repeated testing until no sperm are seen, up to one-third of
patients have rare non-motile sperm (RNMS) in the PV semen analysis.
Presence of RNMS is the most common call a laboratory will receive regarding
PV results. Repeated RNMS is generally considered consistent with a
successful vasectomy.2
—Dean Morbeck, PhD
Director
Fertility Testing Laboratory
Mayo Clinic
Rochester, MN
References
- World Health Organization: WHO laboratory manual
for the examination of human semen and sperm-cervical mucus interaction,
4th edition. Cambridge, UK. Cambridge University Press, 1999.
- Chawla A, Bowles B, Zini A. Vasectomy Follow-Up:
Clinical Significance of Rare Nonmotile Sperm in Postoperative Semen
Analysis. Urology 2004;64:1212-1215.
Brad S. Karon, MD, PhD, is assistant professor of
laboratory medicine and pathology, and director of the Hospital Clinical
Laboratories, point-of-care testing, and phlebotomy services at Mayo
Clinic in Rochester, MN.